1. Field of the Invention
This invention relates to a heat resistant adhesive composition and more particularly to a heat resistant, epoxy resin-based adhesive composition which is satisfactory in operativeness and workability and will retain its high adhesive strength even at a high temperature of 150.degree. to 250.degree. C. or higher after it is cured.
2. Prior Art
Epoxy resin-based resins using aromatic diamines or the like as curing agents have heretofore been widely known as adhesives having excellent heat resistance. However, they are not necessarily satisfactory with respect to adhesiveness at high temperatures.
On the other hand, other heat resistant adhesives which have been well known, include polyamide-based, polyamideimide-based and polybenzimidazole-based adhesives. However, they raise problems from the viewpoint of practical use for the following reasons:
1. Almost all of these adhesives are solvent type adhesives containing high boiling solvents and they therefore need a step of removing the solvent at high temperatures.
2. The uniformity of cured adhesive layers is not always assured since the original adhesives produce by-products such as water when they are cured.
3. The procedure of adhesion using the adhesives is complicated and, in addition, the temperature necessary for adhesion using them is as very high as at least 250.degree. C.
4. The adhesive strength obtained is low.
The known epoxy resin-based adhesives have been used as those having comparatively high heat resistance, however, satisfactory adhesive strength is not obtained at the present with them at a temperature of 150.degree. C. or higher even if they are varied in resin structure or the curing agents used are varied in kind.
Recently, new heat resistant resins have been developed and have partly been studied in attempts to use them as adhesives. Among the new resins is an epoxy resin prepared from triglycidyl ether of trisphenol. The epoxy resin so prepared has, per se, considerably satisfactory heat resistance in a high-temperature region at 150.degree.-250.degree. C., but it will decrease in adhesive strength when it is subjected to impact or shearing force under heat, this proving that it has unsatisfactory adhesive strength.
Therefore, it is a general object of this invention to overcome the disadvantages described hereinbefore.
It is a further object of this invention to provide an adhesive composition which dispenses with a solvent, achieves adhesion using a simplified procedure from the viewpoint of improvement in operativeness and workability and can be used as an adhesive particularly at the site where heat resistance is required.
These and other objects will be apparent from the following description.